This disclosure relates to a non-railbound vehicle propulsion system comprising a combustion engine, an exhaust aftertreatment system connected to the combustion engine, and an electrical power collector for intermittently collecting electrical power from an external power supply track during driving of the vehicle. The disclosure also relates to a method for heating at least one component of a vehicle exhaust aftertreatment system and/or a combustion engine of a vehicle propulsion system by means of an electrical heating system. The vehicle propulsion system and corresponding method may be implemented in many types of road and off-road vehicles, such as trucks, busses, cars, construction vehicles, and the like.
It is known to provide hybrid-electric vehicles with an electrical power collector that is arranged to be connectable to an external power supply track during driving of the vehicle for withdrawing electrical power from said external power supply track. Such a device is for example known from U.S. Pat. No. 5,582,262. This type of vehicle propulsion systems have the advantage of being able to access relatively low cost electrical energy from an external source when driving along a travel path having power supply track, but without being bound to the limited availability of the power supply tracks. The need of a complex and costly battery pack is also reduced due to the sliding connectability to the power supply track during driving of the vehicle.
Prior art vehicle propulsion system with electrical power collectors is however yet fully developed and further improvements in performance are possible.
It is desirable to provide a non-railbound vehicle propulsion system comprising an electrical power collector for collecting electrical power from a power supply track having improved performance.
The disclosure concerns a vehicle propulsion system comprising a combustion engine, an exhaust aftertreatment system connected to the combustion engine, and an electrical power collector for intermittently collecting electrical power from an external power supply track during driving of the vehicle.
The disclosure is characterized in that the vehicle propulsion system comprises a heating system that is arranged to heat at least one component of the exhaust aftertreatment system and/or the combustion engine and that the electrical power collector is arranged for supplying the heating system with electrical power when collecting electrical power from the external power supply track.
When the vehicle propulsion system is powered by electrical energy from the power supply track the operation of the combustion engine of the vehicle propulsion system may be stopped for improved fuel efficiency. However, as to result of the stopped operation of the combustion engine, the combustion engine and the exhaust aftertreatment system cools down. When the vehicle propulsion system upon reaching the end of the power supply track subsequently must switch over to combustion engine propulsion again the combustion engine and/or exhaust aftertreatment system may exhibit a temperature below its normal working temperature, such that the performance is reduced. Similarly, the maximal power output of the electrical traction machine of the vehicle propulsion system may be selected to suffice as sole propulsion source only up to certain road inclinations but require additional propulsion power from the combustion engine during climbing of larger road inclinations, for the purpose of attaining a more cost-effective overall propulsion system. Also this kind of system will thus potentially suffer from a low temperature of components of the exhaust aftertreatment system and/or combustion engine at engine start-up.
A sudden switch from a stopped cold engine to a running engine with significant load may have detrimental effect to the engine in terms of service requirements. A cold engine having cold lubrication oil does not exhibit as good lubrication performance as a warm lubrication oil, thereby shortening the lift time of bearings, pistons, cylinders, and the like. Other parts of the engine that may be damaged if operating an engine at high load and with cold lubrication oil are the oil pump and the oil filter, which may not be dimensioned to withstand the elevated pressure caused by the high viscosity of cold lubrication oil.
Modern catalytic-based exhaust aftertreatment systems are often highly dependent on having a certain operating temperature to attain a sufficient catalytic process. For example, the use of selective catalytic reduction (SCR) for reducing NOx emissions is widespread within the automotive industry, with the most common technology using urea (NH2CONH2) as a precursor to ammonia (NH3) for the catalytic removal of NOx emissions by converting a mixture of NOx and ammonia (NH3) into nitrogen gas (N2) and water (H2O). However, the NOx abatement efficiency of an SCR catalyst has two-fold temperature dependence, limiting the efficiency during low-temperature exhaust conditions. The reaction rates of the catalytic reactions for NOx removal are dependent on temperature, with an active temperature window generally starting at a catalyst temperature of e.g. 150° C., depending also on the NO:NO2 ratio of the feedgas NOx emissions. Moreover, in case urea is employed as reductant for SCR, the decomposition reactions, i.e. thermolysis and hydrolysis of urea to produce gaseous ammonia and carbon dioxide, are highly dependent on temperature. If the exhaust temperature upstream the SCR catalyst is below a certain level, e.g. 200° C., there is a risk for incomplete urea decomposition, thus limiting the NOx removal efficiency. There is also a risk for formation of unwanted solid by-products through polymerization reactions, causing, clogging of the SCR catalyst and an increased back pressure of the exhaust aftertreatment system. Clearly, a sudden switch from a stopped engine and a cold exhaust after-treatment system to a running engine will temporarily result in high NOx emission levels, until the operating temperature of the exhaust aftertreatment system has reached a sufficiently high temperature, such as about 150-200° C.
The problem of cold engine and/or cold exhaust aftertreatment system may be efficiently solved in that the vehicle propulsion system comprises a heating system that is arranged to heat at least one component of the exhaust aftertreatment system and/or the combustion engine. The electrical power collector of the vehicle propulsion system is arranged for supplying the heating system with electrical power when collecting electrical power from the external power supply track for cost-effective heating.
Without the heating system powered by electrical energy from the external power supply track, the exhaust emission reduction performance would be low during as certain initial time period because the operating temperature of the exhaust aftertreatment system would be below the threshold value. Alternatively, the combustion engine would have to be operated in a combustion mode a certain time period before reaching the end of the external power supply track for the purpose of heating the engine and exhaust aftertreatment system, thereby resulting in reduced fuel economy performance. Hence, the provision of an electrical heating system powered by electrical energy from the external power supply track results in improved performance of the vehicle propulsion system.
The disclosure also concerns a method for heating at least one component of a vehicle exhaust aftertreatment system and/or a combustion engine of a vehicle propulsion system by means of a heating system, wherein the vehicle propulsion system comprises an electrical power collector for intermittently collecting electrical power from an external power supply track during driving of the vehicle. The method comprises the step of supplying the heating system with electrical power from the electrical power collector when collecting electrical power from the external power supply track, thereby enabling improved performance.
Further advantages can be achieved through aspects of the present invention.
The vehicle propulsion system may comprise an electrical traction machine for propulsion of a hybrid electric vehicle and operation of the combustion engine may be configured for being stopped during at least part of the time when collecting electrical power from the external power supply track during driving, of the vehicle. By using mainly the electrical traction machine as propulsion means during collecting electrical energy from the power supply track and keeping the combustion engine in a stopped, stillstanding mode, significant fuel saving and emission reduction may be accomplished.
The vehicle propulsion system may comprise vehicle relative position determining means that is arranged to determine vehicle position in relation to power supply track availability. The vehicle relative position determining means may primarily be arranged to compare present geographic vehicle propulsion system position with stored data concerning geographical power supply track installation, and based thereon determine present and future vehicle position in relation to power supply track availability for the presently selected travel path. Possibly, the vehicle relative position determining means may also or alternatively include some type of dedicated short-range communication means located on the vehicle propulsion system and at least partly along the power supply track for locally, without knowledge of present geographic position, in real-time determine if the external power supply track is available at present vehicle position.
The electrical power collector may be arranged to collect electrical power while being in sliding contact with an electrical conductor of the power supply track, or by inductive, contact-less coupling between the electrical power collector and the power supply track. Sliding contact may be realised having power supply track positioned embedded in the ground, or above but adjacent to the ground, or at an elevated position above the road or travel path for driving. Inductive coupling may be realised by providing electrical conductors in or on the ground, or on any side of the vehicle. Sliding contact generally exhibits a higher power transfer efficiency factor than inductive coupling, but also higher demands on the power collector performance, higher wear and higher maintenance requirements.
The heating system may be arranged to heat the at least one component of the exhaust aftertreatment system and/or the combustion engine by means of at least one electrical heater, which comprises at least one electric resistive member that is arranged to convert electrical energy to heat. An electrical heater using an electric resistive member is a cost-effective and reliable solution for heating. An electric resistive member is generally also relatively small enabling compact installations.
The electric resistive, member may be fastened to, and arranged to conduct heat directly to the at least one component of the exhaust aftertreatment system and/or the combustion engine. This design solution enables a compact installation with few modifications of the present exhaust aftertreatment system layout. Service and repair of the exhaust aftertreatment system is also not negatively influenced to a significant degree. The electric resistive member may comprise a metal wire or strip, or a ceramic material. The wire, strip or ceramic material may be attached to an exterior surface of the component to heat, or be embedded within the component. The ceramic material may as such form a component of the component to heat, or may be laminated to a material part of the component.
The at least one electric resistive member may be arranged to heat a fluid heat transport medium, such as air, and the fluid heat transport medium may be arranged to heat the at least one component of the exhaust aftertreatment system and/or the combustion engine. The electric resistive member may consequently be spaced apart from the component, and a heat carrier, for example air, carries the heat from the electrical heater to the engine and/or component of the exhaust aftertreatment system. This may be solved practically in many ways. For example, the at least one component of the exhaust aftertreatment system and/or the combustion engine may be substantially enclosed by a common or individual housing that defines at least one cavity between the housing and the at least one component of the exhaust aftertreatment system and/or the combustion engine, which at least one cavity may be filled the fluid heat transport medium. Typically, heated air within the cavity or supplied to the cavity may thus heat the components of the exhaust aftertreatment system and/or the combustion engine. Alternatively, the exhaust aftertreatment system may comprise at least one flow junction for allowing the heated fluid transport medium to enter inside the at least one component of the exhaust aftertreatment system. Still more alternatively, a flow of heated fluid transport medium may simply be directed towards an exterior surface of the at least one component of the exhaust aftertreatment system and/or the combustion engine.
A control unit may be arranged to control operation of the heating system based on the determined vehicle relative position. This enables many alternative intelligent heating strategies of the at least one component of the exhaust aftertreatment system and/or the combustion engine, thereby enabling improved energy efficiency, performance and reduced emissions. For example, the control unit may be arranged to coordinate operation of the heating system with an estimated time period until the vehicle propulsion system will reach the end of the external power supply track and the present temperature of the associated component or combustion engine, or simply an estimated time period until the combustion engine will be restarted. This coordinated operation of the heating system enables the component or combustion engine to exhibit it predetermined target temperature at time of reaching the end of the external power supply track. The starting time and power output of the electrical heating system is consequently calculated based on the estimated time left until the combustion engine is deemed to restart, as well as the temperature difference between present and target temperature. A stored look-up table or similar may be used for calculating the required heating time.
According to another example, the control of the electrical heating, system based on the determined vehicle relative position may enable a delay of a planned fuel-based regeneration of a exhaust particle filter PF of the exhaust aftertreatment system if an estimated time period until the vehicle propulsion system will reach the start of the external power supply track is within a predetermined time window, and subsequently performs a electricity-based regeneration if the exhaust particle filter when the electrical power collector collects electrical power from the power supply track. The electricity-based regeneration may be realised using solely the electrical heating system or in combination with conventional heating, such as increased exhaust gas temperature by supply of unburned hydrocarbons to the exhaust system. By delaying the planned fuel-based regeneration of an exhaust particle filter and subsequently using the electrical heating system for the regeneration results in improved fuel-economy and reduced costs.
The vehicle propulsion system may comprise a control unit that is arranged to control operation of the heating system based on present temperature of the associated component or combustion engine. This heating strategy is easily implemented and does not require information about time interval left until reaching the end of the power supply track, or estimated time period until restart of the combustion engine. Instead, the heating system may be controlled to constantly hold the component or combustion engine above a predetermined level, which enables an efficient exhaust aftertreatment system functionality and engine operation upon reaching the end of the power supply track. The control unit may for example determine the present temperature of the associated component or combustion engine by means of at least one temperature sensor positioned on, within and/or adjacent the associated component or combustion engine.
The heating system may be arranged to constantly operate on a predetermined power level when electrical power is supplied from the electrical power collector. This heating strategy is easily implemented and does not require information about time interval left until restart of the combustion engine, and also not about the present temperature of the associated component or combustion engine.
This disclosure also concerns a corresponding method for heating at least one component of a vehicle exhaust aftertreatment system and/or a combustion engine of a vehicle propulsion system by means of an electrical heating system.